The present invention relates generally to fasteners for holding an object against a surface via an interference fit between the fastener and a recess in that surface. More particularly, the present invention relates to pound-in anchor bolts for use in masonry.
This invention is an improvement upon products made by Rawlplug Co., Inc. as well as those made by Illinois Tool Works, Inc. Those products of Rawlplug are described in U.S. Pat. Nos. 4,828,445 and 4,963,062. The full disclosure of these prior patents is specifically incorporated herein by reference, and the reader is directed to review those references initially to obtain background and contextual information. Similarly, the products of Illinois Tool Works (ITW) are described by comparison in the reported decision of Rawlplug Co., Inc. v. Illinois Tool Works Inc., 23 U.S.P.Q. 2d 1054 (S.D.N.Y. 1992). That decision is likewise specifically incorporated by reference herein for background and contextual information.
Briefly, the Rawlplug anchors are characterized by a shank having an intermediate peak with separate opposing bases while the ITW anchors are characterized by an offset of the shank itself at an intermediate location to create peaks with integral bases for the opposing peaks. However, neither of these types of anchors nor other such anchors currently on the market have proven to be entirely satisfactory. Ideally, minimal involvement or distortion of the anchor head and shank orientation would result during installation so that the head when being struck, does not cant off of the recess centerline and, thus, can lie flat against the object or surface when fully installed. Also, the spacial requirements of the anchor should be minimized to reduce materials cost and the necessary masonry penetration depth. At the same time, however, retention pressure should be maximized so as to prevent undesired removal of the anchor from the recess. Further, it is desirable to reduce manufacturing costs as much as possible.
Accordingly, the present invention provides an anchor bolt having a shank which is retained within a recess via peak to peak reaction forces rather than a plurality of peak to base arrangements. This is accomplished through the use of one or more continuous "S" bends or undulations intermediate the shank ends. The "S" bends each create two peaks which extend outwardly from the shank surface with a continuous curve therebetween. That curve includes an inflection point, preferably on the longitudinal axis of the shank, but the slope of the curve at the inflection point is not parallel to that longitudinal axis. Thus, when the shank is inserted within the recess, compressive pressure applied to one such peak is directly opposed by such forces applied to the other peak. These peaks can be disposed on opposite sides of the shank or, for example, disposed in a helical or other such pattern about three or more sides of the shank. Serrations and/or an abrasive surface can also be provided on the shank to increase retention.